Variable tech support

[#1]

I've noticed on the few occasions I actually need tech support a variation in the amount of knowledge and expertise shown by advisors.
I live in the middle of nowhere and my usual d/l speed is only around 2.5Mbs on a good day. Recently it dropped to a steady 1.8Mbs for days, sometimes as low as 1.5Mbs
I contacted tech support and was told that this was within the acceptable range for my connection, the maximum being 2.0Mbs and there was no problem. As to the question why had I been 'enjoying' 2.5Mbs for as long as I could remember he had no answer.
Now I know if my car usually does 40mpg and suddenly drops to 35mpg and I haven't altered my driving habits, whilst it may still fall within the range of fuel consumption figures expected there is something wrong.
I contacted technical support again and spoke to a different advisor. I don't understand the details but he sent me info re S/N ratio and dropouts etc and said he would reset my connection and put it in 'learning mode'.
Within a couple of days my speed had climbed to an unheard of 3.5Mbs and, fingers crossed, still seems stable at that speed.
If at first you don't succeed.................................................................

[#2]

...and if you get the wrong diagnosis, it will fail again.  The question not explored here is why had the SNRM changed?
Put simply, the synch speed and SNRM are figures which are "locked" together - the higher the SNRM, the lower the synch speed for any given line's attenuation.  The SNRM needs to be high enough so that the signal can be "read" without excessive levels of error.  If the error rates are too high, the DLM will raise the SNRM (reduce the speed) until the error rate becomes "acceptable".
You have not provided the router stats as requested / described in the speed issues thread at the top of this forum, so it is not possible to be precise on the details of your situation, however I would suspect that you have had an elevated SNRM for a while and the reset will be short lived.  A reset puts the line into a 10 day training period, during which the DLM will work out the optimal speed for your line.  Do not be surprised if it slows down again, as the cause of it originally slowing down has not been identified.
Note that the cause of slowing lines can come and go, especially if the cause is a dickey cable joint.  Is your phone line quiet?  Did you do a quiet line test - dial 17070 option 2 using a corded phone connected to the master socket.
Is the router connected to the master socket?

[#3]

The first agent you spoke to did an estimate check, possibly because he was untrained on basic faults and as such gave advice based on the results. I would have liked to have thought we'd have done more for you on the first call though - he certainly didn't go "the extra mile".
The second agent did an SNR reset as Townman says. Unfortunately, I have no stats of how your line was before the work was done.